A systematic analysis of the structure, function, and regulation of the pyruvate, alpha-ketoglutarate, and branched chain alpha-keto acid dehydrogenase complexes from microorganisms and from mammalian tissues will be continued. The two regulatory enzymes, pyruvate dehydrogenase kinase and pyruvate dehydrogenase will be further characterized with respect to subunit structure and function. These enzymes, which regulate the activity of the mammalian pyruvate dehydrogenase complex by phosphorylation and dephosphorylation, have been obtained in an essentially homogeneous state. Systematic studies on the reconstitution of the Escherichia coli and mammalian alpha-keto acid dehydrogenase complexes will be continued, particularly with respect to elucidating the molecular basis of the unequal molar ratios of their component enzymes. Comparative studies will be continued on structural and mechanistic similarities and differences between the E. coli pyruvate and alpha-ketoglutarate dehydrogenase complexes, using electron microscopy, limited proteolysis, immunological comparisons and x-ray diffraction. The bovine kidney branched chain alpha-keto acid dehydrogenase complex and its component enzymes will be further characterized.